The goal of rational cancer chemotherapy has become therapies which are active by virtue of the molecular events involved in transformation and which target processes that sustain the transformed phenotype. One of the most common alterations during tumor cell progression is loss of the function of the p53 pathway. Not only is p53 stabilized in response to DNA damage, but it also accumulates in response to nucleotide depletion with agents that cause little if any DNA damage, specifically, the GART class of de novo purine synthesis inhibitors and the de novo pyrimidine synthesis inhibitor PALA (N-phosphonoacetyl-L-aspartate). In this proposal, we would study how nucleotide depletion causes accumulation of p53, the mechanism of the p53 response pathway subsequent to signaling of nucleotide depletion, and the role of co-activators and repressors in this response. This proposal seeks to identify the molecules and mechanisms of the p53 signaling initiated by nucleotide depletion, learn how nucleotide depletion, per se, leads to cell death, and identify if there are survival disadvantages under nucleotide depletion conditions induced by the cancer phenotype that can be used for therapeutics. These studies are a logical extension of past studies supported by this grant, but also represent new directions to therapeutics suggested by recent advances in cancer cell biology.